Process of preparing finely divided iron including electrolysis, washing, wet grinding, and flotation of impurities



PRocEss or PREPARI G FINELY DIVIDED IRON INCLUDING ELECTROLYSIS, WASHING, WET GRINDING, AND FLoTATIoN F IMPURITIES Friedrich W. Czech, Painesville, Ohio, assignor to Dian}o6g Alkali Company, Cleveland, Ohio, a corporation 0 10 No Drawing. Application January 3, 1956 Serial No. 556,778

7 Claims. (Cl. 204-40) This invention relates to a new and improved method of preparing finely-divided metal, and more particularly relates to a new and improved process for electrolytically producing powdered iron of high purity.

. Finely-divided metals or so-called powdered metals,

as referred to hereinafter, are achieving an increasing commercial importance because they have certain advantages not shared by metals employed in other forms. Metal articles prepared by powder metallurgy techniques, characterized by high density, approaching or equalling that of cast metals, are formed by compressing at high pressure a charge of powdered metal into a die or mold of the desired shape. The thus-obtained compact, having an unfired or fgreen strength sufiicient to prevent breakage during handling, is then fired or sintered at an elevated temperature to obtain a maximum strength.

Powder metallurgy provides significant savings to industryby elimination, or substantial reduction; of machining operations, reduction in handling, substantial elimihation of scrap metal in the form of matching waste, and obtention of extremely close tolerances in compacted and sintered parts. Not only can a large number of machining and other processing steps heretofore considered essential in the fabrication of metal parts be eliminated, but also, in many instances, use of metallic powders permits the development of unusual and desired physical andrnechanical properties not available in parts formed by other techniques.

While the applicability of powdered metals is increasing, and their use becoming more widespread, e. g., in bearings, including so-called oil-less bearings, electrical cores and other components of electronic circuitry, as well as in mechanical parts such as gears, cams and the like,

the production of the metal powder itself, notably high purity iron powder, has continued to present certain problems which have combined to require a premium price for a satisfactory product, and which, in some instances, have not heretofore been completely overcome.

H Up to thepresent time, iron powder has been difficult to manufacture to the increasingly high standards and close specifications imposed by industry, in calling for a generally useful iron powder having satisfactory compressability, density, fiowability and particle size distribution, Accordingly, when iron powder of a high quality has been desired, it generally has been rather costly since the steps of preparation and the purification operations have been numerous and costly, and since often the yield of a suitable material has been relatively low.

, THE PRIOR ART Typical of prior methods of obtaining powdered iron powder, at times these prior electrolytes have been difficult and/or costly to operate and maintain. In some instances, the electrolytes heretofore utilized have been 2 highly viscous under operating conditions, thus increasing problems associated with agitation and mechanical drag out of the electrolyte with resulting contamination of the product and lowered op'era'ting efiiciency.

OBJECTS OF THIS INVENTION It is a principal object of this invention to provide a new and improved process for electrolytically producing a high quality iron powder.

A further object of this invention is to provide an improved iron powder of high purity and advantageous processing characteristics in powder metallurgy applications.

A still further object of this invention is to provide a new and improved method of recovering and purifying metal powder. V

These and other objects and advantages of the invention will appear more fully from the following description thereof.

THE PRESENT INVENTION This invention contemplates the preparation of high quality, finely-divided iron by electrolyzing soluble iron dissolved from an iron compound suspended in an elec' 'trolyte consisting essentially of an alkali metal hydroxide dissolved in water, separating iron oxide from the thusobtained electrodeposit by flotation and recovering the desired finely-divided iron;

More specifically, the method of this invention comprises preparing finely-divided iron by electrolyzing soluble iron dissolved from an iron compound suspended in an electrolyte, by agitation, the electrolyte consisting essentially of an alkali metalhydroxide dissolved in water, washing the thus-obtained electrodeposit, preferably with water, to remove entrained alkali metal hydroxide and iron compounds and separating iron oxide from the washed electrodeposit preferentially suspending the iron oxide in a volatile organic liquid and recovering finelydivided iron in substantially pure form.

In practice, this invention also contemplates comminuting the electrodeposit, after removal of entrained alkali metal hydroxide and iron compounds therefrom, prior to removal or iron oxide by flotation, when the particle size distribution obtained by electrolysis requires alteration of the particle size to meet a particular specification.

A preferred practice of this invention comprisesthe successive steps of (1) suspending in an aqueous solution of an alkali metal hydroxide at least one iron oxide, (2) passing an electric current from an anode to a cathode through this solution to electrolyze soluble iron and deposit it on the cathode in a loosely adherent form, (3) washing the thus-obtained electrodeposit to remove entrained iron oxide and alkali metal hydroxide, (4) immersing the washed electrodeposit in a volatile organic liquid and while in contact with the organic liquid effecting, if needed, any grinding or other comminuation to obtain the desired particle size distribution, (5) agitating the product of step (4) with the same or a different volatile organic liquid preferentially to suspend iron oxide and other retained impurities, if any, having a density less than that of iron, and (6) separating and recovering the finely-divided iron.

The expression volatile organic liquid" as used throughout the specification and claims is intended to refer to various volatile organic liquids capable of preferentially suspending, without adverse chemical efle'cts, iron oxides when a mixture of finely-divided iron and iron oxide are agitated therewith. A presently preferred group of volatile organic liquids are the lower aliphatic alcohols including straight and branched chain alcohols containing up to about twelve carbon atoms. Illustrative alcohols are methyl, ethyl, propyl, butyl, and corre- 3 sponding branched chain alcohols, e. g., isopropyl, isobutyl, and the like, it being understood that a highly purified alcohol need not be employed in all instances, at times, a technical grade alcohol being entirely satisfactory.

It will be appreciated that the practice of this invention may be conducted as a batch operation with recycling of the alcohol or other organic fluid after such intermediate filtration, centrifugation, distillation or the like as necessary. It will also be appreciated, however, that the practice of this invention can be advantageously conducted as a continuous operation wherein treatment of electrodeposited iron with a volatile organic liquid is accomplished using a continuous concurrent or countercurrent feed of oxide-contaminated product and alcohol or other organic liquid and continuous discharge of purified iron and iron oxide.

The electrolyte consists essentially of an alkali metal hydroxide dissolved in water, the expression alkali metal hydroxide as used throughout the specification and claims being intended to include hydroxides of the several. alkali metals, i. e., sodium, potassium, lithium, cesium, and rubidium. However, those skilled in the art will realize that sodium hydroxide and potassium hydroxide are the most readily available alkali metal hydroxides and that sodium hydroxide is perhaps the most common of the alkali metal hydroxides. For that reason, particular emphasis is hereinafter made to sodium hydroxide although the invention is not so limited.

The iron compound, comprising the source of the electro-deposited iron, electrolyzed in the practice of this invention generally may comprise one or a mixture of several types of iron compounds, preferably iron oxides, including relatively impure iron oxides as embodied in iron ores. Hence, it will be understood that the expression iron compound as used throughout the specification and claims is intended to include ferrous oxide, ferric oxide, various iron ores such as Red Ochre, Oolitic hematite, magnetite, limonite, siderite, and/ or mixtures of iron ores and/ or iron oxides in either a purified or relatively impure form. The presently preferred iron compound is Fe O The following are illustrative analysis of iron ores from which finely-divided iron can be obtained by the practice of this invention wherein the contents are indicated in terms of percent by weight:

0. P Ore A Ore B Ore C Ore D Ore It is preferred to employ an electrolyte consisting essentially of about 35 to 50% by weight of an alkali metal hydroxide, preferably sodium hydroxide, and 65 to 50% by weight water, this water-alkali metal hydroxide mixture containing about 5 to 10% based on the weight of the alkali metal hydroxide, of an iron compound, preferably an iron oxide, superior results as to purity generally being obtained when a chemically pure ferrous oxide, ferric oxide and/ or mixtures of these or other iron oxides are employed, although the practice of this invention is advantageous as a means of obtaining a high purity product even when a relatively impure source of iron, e. g., iron ore, is utilized. These quantities of electrolyte ingredients may at times be varied outside the preferred limits. For example, in some instances the concentration of the iron compound may exceed 10%, the upper limitation on the amount of iron compound employed being that at which effective suspension of iron compound in the electrolyte is prevented.

Similarly, concentrations of the added iron compound of lower than 5% also can be used. In fact, it is a feature of this invention to maintain the desired concentration of dissolved iron in solution by additions of relatively small amounts of the same or different iron compounds. Such additions insure in the electrolyte a constant source of suspended, undissolved iron compound capable of dissolving as the chemical equilibrium and solubility conditions permit to provide dissolved iron in the electrolyte electrodeposition on the cathode.

Thus, it will now be understood that a preferred practice of this invention contemplates electrolytically preparing a finely-divided iron of high purity by the successive steps of passing an electric current, preferably a low voltage direct current, from an anode to a cathode through an electrolyte consisting essentially of about 35 to 50% by weight sodium hydroxide and about 65 to 50% by weight water, and about 5 to 10%, based on the weight of sodium hydroxide of an iron oxide, preferably FeO, Fe O or mixtures thereof as occur in iron ores, to obtain a readily removable electrodeposit on the cathode, washing the electrodeposit with water to remove entrained iron oxide and alkali metal hydroxide, and separating iron oxide from the resultant material by agitation of the material with volatile organic liquid, preferably a lower alcohol, to remove iron oxide by flotation and subsequently to recover finely-divided iron powder.

ELECTROLYSIS CONDITIONS The following summarizes the foregoing conditions of electrolysis and indicates the preferred conditions under which a desirable electrodeposit is obtained in accordance with this invention:

Preferred Source of iron C. P. FezOa.

Iron oxide concentration. 510% of alkali metal hydroxide.

Particle size of iron compound mesh.

Agitation Vigorous to maintain uniform dispersion of iron compound but insuflicient to dislodge the electro-deposlt.

In a preferred embodiment of the invention, the iron powder obtained as an electrodeposit during the electrolysis is removed from the cathode by scraping, brushing, chipping and the like, and directly immersed in a volatile organic liquid in which it is then ground by ball milling, or the like, to obtain the desired particle size distribution. In practice, the volatile organic liquid may be recovered by filtration or distillation, and recycled if desired, or employed in the subsequent flotation step. Thus, it will be understood that a preferred practice of this invention contemplates both the immersion of the electro-deposited iron, after washing with water to remove entrained iron oxide and alkali metal hydroxide in a lower aliphatic alcohol, grinding the iron powder, if necessary, While wet with this alcohol and subsequently effecting removal of retained iron oxide by flotation and recovering the iron powder in a highly purified state. 1

In order that those skilled in the art may more com pletely understand the present invention and the preferred methods by which the same may be carried into effect, the following specific examples are offered:

Example 1 PART A To illustrate the practice of this invention, an electrolytic cell is prepared by placing alternatingly spaced (2") electrodes (2 iron cathodes%" x 22%" x 10" and 3 nickel anodes x 8 x 22 /2") in a. tank (18% x 8 /2 x 29") of nickel. There is introduced sufficient of an electrolyte prepared by mixing 200 lbs. of 50% sodium hydroxide solution and 12 lbs. C. P. Fe O; (iron oxide: anhydrous NaOH ratio of 0.12:1.0)

to submerge the electrodes. While the electrolyte is vigorously agitated, a direct current (current density of 0.31 amp./eq. in.) is passed from anode to cathode through the electrolyte for 20 hours, the electrolyte being maintained at a temperature of 190 F. and 2 lb. additions of C. P. Fe O made each 4 hours during electrolysis. There is obtained a loosely adherent electrodeposit on the cathode.

PART B The cathodes are removed and washed with cold water for ten minutes until the water runs clear. The thus-washed electro-deposit (about /s thick) is then scraped from the cathode and immersed in ethyl alcohol. The electrodeposit slurry is then ball milled for 12 hours using agate balls. From the thus-obtained ground product fines (-100 mesh) are removed and coarse material ground further. The ground material is then covered with ethyl alcohol and agitated until all material is suspended. The agitation is then stopped and the finelydivided iron settles rapidly while iron oxide remains suspended. The iron is removed and the process repeated 4 times using ethyl alcohol. The iron is then dried at 110 C. for 2 hours. The thus-obtained product has the following chemical and screen analysis:

As determined in accordance with Standard 2-48, Method for Deter minationfioi Hydrogen Loss of Metal Powder, of Metal Powder Association (195 Example II PART A In a 1000 ml. beaker are arranged a 1" x 5" x 1 nickel cathode and a 2" x 5" x ,4, nickel anode spaced 2" apart. To establish an electrolytic cell, there is added to the beaker 800 ml. of 50% by weight sodium hydroxide and 50 gms. of C. P. Fe O (approximate ion oxidezanhydrous NaOH ratio of 0.1:1.0). The electrolyte is then heated to, and maintained at, a temperature of 180 F. with continuous vigorous agitation to keep undissolved iron oxide suspended. A direct current (2.5 amperes) is then passed from anode to cathode through the electrolyte for 23.5 hours at a current efiiciency of 80%. There results a loosely adherent electrodeposit which can readily be removed from the cathode.

PART B The product of Part A is then treated in accordance with the procedure of Example I, Part B and an equally advantageous iron powder is obtained.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. The method of preparing a high quality, finelydivided iron which comprises electrolyzing soluble iron dissolved from an iron compound suspended in an electrolyte consisting essentially of an alkali metal hydroxide dissolved in water, thereby to form a loosely adhering deposit including iron at the cathode, removing the iron deposit and insoluble iron compounds associated therewith from the cathode, separating insoluble iron compounds from the thus-obtained electrodeposit by flotation and recovering therefrom finely-divided iron.

2. The method of preparing a high quality, finelydivided iron which comprises electrolyzing soluble iron dissolved from an iron compound suspended in an electrolyte consisting essentially of an alkali metal hydroxide dissolved in water, thereby to form a loosely adhering deposit including iron at the cathode, washing the thusobtained electrodeposit, removing the electrodeposit 01' iron and insoluble iron compounds associated therewith from the cathode, separating insoluble iron compounds from said electrodeposit by flotation, and recovering the finely-divided iron.

3. The method according to claim 2 wherein the washing is with water.

4. The method according to claim 2 wherein the flotation is accomplished by preferentially suspending the insoluble iron compounds in a volatile organic liquid.

5. The method of electrolytically preparing a finelydivided iron of high purity, said method comprising the successive steps of passing an electric current from an anode to a cathode through an electrolyte consisting essentially of sodium hydroxide dissolved in water, and minor amount of an iron compound, to obtain a loosely adherent electrodeposit on said cathode, washing said electrodeposit with water to remove entrained iron compounds and said sodium hydroxide, removing the metallic iron deposit and insoluble iron compounds associated therewith from the cathode, immersing the thus-washed deposit in a volatile organic liquid and separating insoluble iron compounds therefrom by suspending said iron compounds in a volatile organic liquid, and removing substantially pure iron therefrom.

6. The method according to claim 5 wherein the washed electrodeposit is ground to the desired particle size while covered with said organic liquid.

7. The method of electrolytically preparing a finelydivided iron of high purity which comprises the successive steps of passing a direct electric current from an anode to a cathode through an electrolyte consisting essentially of about 35 to 50% by weight of sodium hydroxide, 65 to 50% by weight water and about 5 to 10% of at least one iron oxide, based on the weight of sodium hydroxide, to obtain a readily removable electrodeposit on said cathode, washing said electrodeposit with water to remove entrained iron oxide and alkali metal hydroxide, from the cathode removing the material deposited by said current, grinding the Washed electrodeposit while in contact with a lower aliphatic alcohol to the desired particle size, separating iron oxide from the resultant material by agitating the ground product with a lower aliphatic alcohol and removing substantially pure iron therefrom after flotation of iron oxide away from the iron.

References Cited in the file of this patent UNITED STATES PATENTS 1,462,421 Pearson et al. July 17, 1923 1,569,484 Hall Jan .12, 1926 1,657,161 Higginbotharn Jan. 24, 1928 1,895,505 Wuensch Jan. 31, 1933 2,027,532 Hardy Jan. 14, 1936 2,064,109 Hadsel Dec. 15, 1936 2,194,026 Mandle Mar. 19, 1940 2,327,402 Clark Aug. 24, 1943 2,389,734 Mehl Nov. 27, 1945 2,480,156 Matson Aug. 30, 1949 U S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE QF CORRECTION Patent No, 2,824,052 February 18, 1958 Friedrich Wa Czech It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as oorrected below.

Column 1, line 34-, for matching" read =maehining column 2, line 43, for "removal or" read ==removal of===3 column 5, line 3, for "eqo in," read sqo ina o Signed and sealed this 6th day of May 1958,

(SEAL) Attest:

KARL EL AXLINE ROBERT C. WATSON attesting Officer issioner of Patents 

1. THE METHOD OF PREPARING A HIGH QUALITY, FINELYDIVIDED IRON WHICH COMPRISES ELECTROLYZING SOLUBLE IRON DISSOLVED FROM AN IRON COMPOUND SUSPENDED IN AN ELECTROLYTE CONSISTING ESSENTIALLY OF AN ALKALI METAL HYDROXIDE DISSOLVED IN WATER, THEREBY TO FORM A LOOSELY ADHERING DEPOSIT INCLDUDING IRON AT THE CATHODE REMOVING THE IRON DEPOSIT AND INSOLUBLE IRON COMPOUNDS ASSOCIATED THEREWITH FROM THE CATHODE, SEPARATING INSOLUBLE IRON COMPOUNDS FROM THE THUS-OBTAINED ELECTRODEPOSIT BY FLOTATION AND RECOVERING THEREFROM FINELY-DIVIDED IRON. 